Response Mechanism of Sediment Organic Matter of Plateau Lakes in Cold and Arid Regions to Climate Change: a Case Study of Hulun Lake, China

Lake organic matter is one of the important forms of terrestrial carbon, and its sedimentary evolution is affected by many factors such as climate and source. However, few studies have been conducted on the bidirectional feedback mechanism between the sedimentary evolution of organic matter and climate change in cold and arid lakes. Historical variations of the sediment organic matter (SOM) and source construction of Hulun Lake, a typical lake in the cold and arid region of China, were studied by multiple methods. The interactions and feedback mechanisms between the sedimentary evolution, climate change, and source construction change were also discussed. Overall, the characteristic indexes of the SOM showed obvious and uniform characteristics of periodical changes. The indexes were relatively stable before 1920, and fluctuated from 1920 to 1979. Since the 1980s, the total organic carbon, carbon stable isotope, and fluorescence intensity of the protein-like component in the water extractable organic matter in the SOM has increased, while the carbon to nitrogen ratio decreased. The absolute dominant contribution of terrestrial source to the SOM had changed, and the relative average contribution rate of autochthonous source increased from 17.6% before 1920 to 36.9% after 2000. The increase of temperature, strong evaporation concentration effect, and the source construction change are the important driving factors of the sedimentary evolution of organic matter in Hulun Lake.

Differences in the Composition, Source, and Stability of Suspended Particulate Matter and Sediment Organic Matter in Hulun Lake, China

Sediment (SOM) and suspended particulate (SPOM) organic matters are two important organic matters in water. Their occurrence, migration and transformation, and stability have important effects on the environmental behaviors of carbon, nitrogen, phosphorus, and other pollutants in a water environment. The content, composition, fluorescence characteristics, source, and stability of SOM and SPOM in Hulun Lake, a typical lake in cold and arid region of China, were compared by sequential extraction, three-dimensional fluorescence spectroscopy, parallel factor technique, carbon–nitrogen ratio, and stable carbon isotope. SOM and SPOM in north and west were higher than those in east and south. The average content of SPOM (24.70 ± 4.63 g/kg) was slightly higher than that of SOM (23.04 ± 10.27 g/kg), but the difference was not significant. Humin was the dominant component in SOM and SPOM, accounting for 73.7% and 61.2%, respectively. Humus was the main fluorescence component of water-extractable organic matter in SOM and SPOM, accounting for 79.9% and 70.4%, respectively, of the total fluorescence intensity. SOM and SPOM were derived from terrestrial sources with relative contribution rate of about 70%. SPOM was more influenced by autochthonous sources and had significantly lower humification degree and stability than SOM. Effects of climate changes on migration, transformation, stability, and bioavailability of organic matters and endogenous pollutants closely related to organic matters in lakes of cold and arid regions should be paid attention in the future.

Methylobrevis albus sp. nov., isolated from freshwater lake sediment

An aerobic, Gram-stain-negative, rod-shaped bacterium with flagellum, designated L22T, was isolated from freshwater of Hulun Lake, Inner Mongolia, China. The organism was found to grow optimally at 30 ℃ in medium containing 0-0.75%(w/v) NaCl at pH 7.5. The major fatty acid identified was summed feature 8 (C16:1ω7c). The dominant polar lipids were phosphomonoester, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylcholine. The main ubiquinone was Q-10. The G + C content of genomic DNA was 69.8 mol%. The 16S rRNA gene sequences indicated that strain L22T was affiliated with the genus Methylobrevis within the family Pleomorphomonadaceae, being most closely related to M. pamukkalensis JCM 30229T with 95.9% sequences similarity. Based on taxonomic results in this study, we proposed that strain L22T was placed into a novel species in the genus Methylobrevis of the family Pleomorphomonadaceae, for which the name Methylobrevis albus sp. nov. is proposed. The type strain is L22T (= KCTC 72858T = MCCC 1H00432T).